Methods of forming oscillator systems having annular resonant circuitry

ABSTRACT

Systems and apparatus are provided for solid-state oscillators and related resonant circuitry. An exemplary oscillator system includes an amplifier having an amplifier input and an amplifier output and resonant circuitry coupled between the amplifier output and the amplifier input. In exemplary embodiments, the resonant circuitry includes an annular resonance structure that is substantially symmetrical and includes a pair of arcuate inductive elements. In accordance with one or more embodiments, the resonant circuitry includes an additional inductive element that is capacitively coupled to the annular resonance structure via an air gap to improve the quality factor of the resonant circuitry.

RELATED APPLICATION

This application is a divisional of co-pending U.S. patent applicationSer. No. 13/194,714, filed on Jul. 29, 2011.

TECHNICAL FIELD

Embodiments of the subject matter described herein relate generally toelectronic circuits, and more particularly, embodiments of the subjectmatter relate to resonant circuitry for microwave oscillators.

BACKGROUND

Magnetrons are commonly used to generate microwaves in microwave ovensor other microwave application. While magnetrons are well suited forthis purpose, they typically require a relatively high voltage powersource (e.g., 4 kilovolts or more) for operation. Additionally, thelifetime of some magnetrons may be limited or the magnetrons mayotherwise be susceptible to output power degradation over extendedperiods of operation.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the subject matter may be derived byreferring to the detailed description and claims when considered inconjunction with the following figures, wherein like reference numbersrefer to similar elements throughout the figures.

FIG. 1 is a block diagram of an exemplary oscillator system inaccordance with one embodiment of the invention;

FIG. 2 is a top view of exemplary resonant circuitry suitable for use inthe oscillator system of FIG. 1 in accordance with one embodiment of theinvention;

FIG. 3 is block diagram of another exemplary oscillator system suitablefor use with the resonant circuit of FIG. 2 in accordance with oneembodiment of the invention; and

FIG. 4 is a top view of another exemplary embodiment of resonantcircuitry suitable for use in the oscillator system of FIG. 1 or theoscillator system of FIG. 3.

DETAILED DESCRIPTION

The following detailed description is merely illustrative in nature andis not intended to limit the embodiments of the subject matter or theapplication and uses of such embodiments. As used herein, the word“exemplary” means “serving as an example, instance, or illustration.”Any implementation described herein as exemplary is not necessarily tobe construed as preferred or advantageous over other implementations.Furthermore, there is no intention to be bound by any expressed orimplied theory presented in the preceding technical field, background,or the following detailed description.

Embodiments of the subject matter described herein relate solid-stateoscillator systems for microwave applications. As described in greaterdetail below, exemplary oscillator systems are realized using anamplifier with a resonant circuit in the feedback path. The resonantcircuit includes a pair of arcuate (or curved) inductive elements thatoppose one another to provide an annular structure. As used herein, an“annular structure” should be understood as referring to a ring-likestructure that has a voided interior, but the annular structure need notbe perfectly circular. In exemplary embodiments, the arcuate inductiveelements have substantially identical and complementary shape and/ordimensions and are capacitively coupled to each other at their opposingends. In accordance with one or more embodiments, a rectangularinductive element is formed proximate one of the arcuate inductiveelements and spaced apart from the respective arcuate inductive elementsuch that rectangular inductive element is capacitively coupled to thearcuate inductive element via the gap capacitance introduced by the airgap between the rectangular inductive element and the arcuate inductiveelement. Although the subject matter is described herein in the contextof microwave frequency applications, the subject matter is not intendedto be limited to any particular frequency range.

FIG. 1 depicts an exemplary embodiment of an oscillator system 100suitable for use in a microwave oven 150. The oscillator system 100includes, without limitation, an oscillator arrangement 102, frequencytuning circuitry 104, bias circuitry 106, output impedance matchingcircuitry 108, and an output interface 110. In an exemplary embodiment,the elements of the oscillator system 100 are configured to produce anoscillating electrical signal at the output interface 110 having afrequency in the microwave frequency range (e.g., 2.45 GHz) with anoutput power of about 100 Watts or more. It should be understood thatFIG. 1 is a simplified representation of an oscillator system 100 forpurposes of explanation and ease of description, and that practicalembodiments may include other devices and components to provideadditional functions and features, and/or the oscillator system 100 maybe part of a much larger electrical system, as will be understood.

In an exemplary embodiment, the oscillator arrangement 102 includes anamplifier arrangement 120, a resonant circuitry 122, amplifier inputimpedance matching circuitry 124, and amplifier output impedancematching circuitry 126. The resonant circuitry 122 is coupled betweenthe output node 116 of the amplifier arrangement 120 and the input node114 of the amplifier arrangement 120 to provide a resonant feedback loopthat causes the amplified electrical signals produced by the amplifierarrangement 120 to oscillate at or near the resonant frequency of theresonant circuitry 122. As described in greater detail below, in anexemplary embodiment, the resonant circuitry 122 is configured toprovide a resonant frequency of 2.45 GHz, or in other words, theresonant circuitry 122 resonates at 2.45 GHz such that the amplifiedelectrical signals produced by the amplifier arrangement 120 at theamplifier output 116 oscillate at or near 2.45 GHz. It should be notedthat in practice, embodiments of the resonant circuitry 122 may beconfigured to resonate a different frequency to suit the needs of theparticular application utilizing the oscillator system 100.

In the illustrated embodiment of FIG. 1, the amplifier arrangement 120is realized as a transistor 130 having an input terminal (or controlterminal) coupled to the amplifier input node 114 and an output terminalcoupled to the amplifier output node 116. In the illustrated embodiment,the transistor 130 is realized as an N-type field effect transistor(FET) having a gate terminal connected to the amplifier input node 114,a drain terminal connected to the amplifier output node 116, and asource terminal connected to a node 142 configured to receive a groundreference voltage for the oscillator system 100. In an exemplaryembodiment, the transistor 130 is realized as a laterally diffused metaloxide semiconductor (LDMOS) transistor. However, it should be noted thatthe transistor 130 is not intended to be limited to any particularsemiconductor technology, and in other embodiments, the transistor 130may be realized as a gallium nitride (GaN) transistor, a MOSFETtransistor, a bipolar junction transistor (BJT), or a transistorutilizing another semiconductor technology. Additionally, in otherembodiments, the amplifier arrangement 120 may be realized using anysuitable amplifier topology and/or the amplifier arrangement 120 mayinclude multiple transistors.

In an exemplary embodiment, the frequency tuning circuitry 104 generallyrepresents the capacitive elements, inductive elements, and/or resistiveelements that are configured to adjust the oscillating frequency of theoscillating electrical signals generated by the oscillator system 100.In an exemplary embodiment, the frequency tuning circuitry 104 iscoupled between the ground reference voltage node 142 and the input node112 of the oscillator arrangement 102. The bias circuitry 106 generallyrepresents the circuit elements, components, and/or other hardware thatare coupled between the amplifier arrangement 120 and a node 140configured to receive a positive (or supply) reference voltage. Inexemplary embodiments, the voltage difference between the supply voltagenode 140 and the ground voltage node 142 is less than 50 Volts. The biascircuitry 106 is configured to control the direct current (DC) ornominal bias voltages at the gate and drain terminals of the transistor130 to turn the transistor 130 on and maintain the transistor 130operating in the saturation (or active) mode during operation of theoscillator system 100. In this regard, the bias circuitry 106 is coupledto the gate terminal of the transistor 130 of the amplifier arrangement120 at the amplifier input node 114 and the drain terminal of thetransistor 130 at the amplifier output node 116. In accordance with oneor more embodiments, the bias circuitry 106 includes temperaturecompensation circuitry configured to sense or otherwise detect thetemperature of the transistor 130 and adjust the gate bias voltage atthe amplifier input node 114 in response to increases and/or decreasesin the temperature of the transistor 130 to maintain substantiallyconstant quiescent current for the transistor 130 in response totemperature variations.

As illustrated, the oscillator arrangement 102 includes amplifier inputimpedance matching circuitry 124 coupled between the resonant circuitry122 at the input node 112 of the oscillator arrangement 102 and theamplifier input 114, wherein the impedance matching circuitry 124 isconfigured to match the input impedance of the amplifier arrangement 120at the amplifier input node 114 to the impedance of the resonantcircuitry 122 and the frequency tuning circuitry 104 at node 112 at theresonant frequency of the resonant circuitry 122. Similarly, theamplifier output impedance matching circuitry 126 is coupled between theamplifier output 116 and the resonant circuitry 122 to match the outputimpedance of the amplifier arrangement 120 at the amplifier output node116 to the impedance of the resonant circuitry 122 at the output node118 of the oscillator arrangement 102 at the resonant frequency.

In an exemplary embodiment, the output impedance matching circuitry 108is coupled between output node 118 of the oscillator arrangement 102 andthe output interface 110, and the output impedance matching circuitry108 is configured to match the input impedance of the output interface110 to the impedance at the oscillator output node 118. The outputinterface 110 generally represents the combination of one or moreantennas, waveguides, and/or other hardware components configured totranslate the oscillating electrical signals at the oscillator outputnode 118 to electromagnetic signals at the oscillating frequency. Forexample, in a microwave oven application where the resonant circuitry122 is configured to provide a resonant frequency of 2.45 GHz, theoutput interface 110 translates the oscillating electrical signals atthe oscillator output node 118 to microwave electromagnetic signals at2.45 GHz and directs the microwave signals into the cooking chamber ofthe microwave oven.

Turning now to FIG. 2, in an exemplary embodiment, the resonantcircuitry 122 of the oscillator system 100 of FIG. 1 is realized asresonant circuit 200. The resonant circuit 200 includes an annularresonance structure 202 and a pair of inductive elements 204, 206. Theannular resonance structure 202 includes a pair of arcuate (or curved)inductive elements 208, 210 that are capacitively coupled at theirlongitudinal ends 212, 214. The arcuate inductive elements 208, 210 aresubstantially identical and complementary in shape, such that thearcuate inductive elements 208, 210 provide a symmetrical annularstructure 202 having a voided interior region 203 when theirlongitudinal ends 212, 214 face or otherwise oppose those of the otherarcuate inductive element 208, 210, as illustrated in FIG. 2. To put itanother way, the arcuate inductive elements 208, 210 are curved inwardtowards one another to provide a symmetrical annular structure 202 thatencompasses a voided interior region 203. By virtue of the inductiveelements 208, 210 being substantially identical in shape, the inductiveelements 208, 210 have substantially identical electricalcharacteristics to provide a relatively high quality factor (or Q value)for the resonant circuit 200. In the illustrated embodiment, the arcuateinductive elements 208, 210 are substantially U-shaped such that theannular resonance structure 202 is substantially rectangular withrounded corners, however, in other embodiments, the arcuate inductiveelements 208, 210 may substantially C-shaped such that the annularresonance structure 202 is substantially circular, as described ingreater detail below in the context of FIG. 4. In this regard, theoverall shape of the annular resonance structure 202 may vary dependingon area or layout requirements or other design constraints for aparticular embodiment. In an exemplary embodiment, the inductiveelements 208, 210 are each realized as a microstrip or anotherconductive material (e.g., a conductive metal trace) formed on anelectrical substrate 201, such as a printed circuit board. The physicaldimensions of the inductive elements 208, 210 are chosen to provide adesired inductance such that the annular resonance structure 202resonates at a desired frequency. For example, the length and width ofthe inductive elements 208, 210 may be chosen such that the annularresonance structure 202 resonates at a frequency of about 2.45 GHz. Inaccordance with one embodiment, to provide a resonant frequency of about2.45 GHz with a conductive metal material (or microstrip) having athickness of about 0.0024 inches, the length 240 of each inductiveelement 208, 210 in a first direction is about 1.03 inches, the length250 of each inductive element 208, 210 in a second direction orthogonalto the first direction is about 0.42 inches, and the width 260 of eachinductive element 208, 210 is about 0.058 inches with an inner radius270 of about 0.121 inches, wherein the width of the air gaps 216, 218between the ends of the inductive elements 208, 210 is about 0.02inches.

As illustrated in FIG. 2, the longitudinal ends 212, 214 of the arcuateinductive elements 208, 210 are spaced apart from one another orotherwise separated to provide air gaps 216, 218 between thelongitudinal ends 212, 214 of the inductive elements 208, 210. In theillustrated embodiment, the resonant circuit 200 includes a pair ofcapacitive elements 220, 222 coupled electrically in series between theinductive elements 208, 210. In an exemplary embodiment, each capacitiveelement 220, 222 is realized as a capacitor, such as a multilayerceramic chip capacitor, that is mounted across the air gaps 216, 218between the longitudinal ends 212, 214 of the inductive elements 208,210 to provide a substantially continuous annular structure. In thisregard, each capacitive element 220, 222 has a first terminal that ismounted, affixed, or otherwise connected to an end 212 of the firstarcuate inductive element 208 and a second terminal that is mounted,affixed, or otherwise connected to the opposing end 214 of the secondarcuate inductive element 210. In this manner, the capacitive elements220, 222 are connected electrically in series between the inductiveelements 208, 210. In an exemplary embodiment, the capacitances of thecapacitive elements 220, 222 are substantially identical and chosenbased on the inductances of the inductive elements 208, 210 such thatthe resonant circuit 200 resonates at a desired frequency. For example,in an exemplary embodiment, the capacitance of the capacitive elements220, 222 is chosen such that the resonant circuit 200 resonates at afrequency of about 2.45 GHz. In an exemplary embodiment, the capacitanceof the capacitive elements 220, 222 is about 2.2 picofarads.

It should be noted that in accordance with one or more alternativeembodiments, the resonant circuit 200 may not include capacitiveelements 220, 222. In this regard, the capacitive coupling provided bythe air gaps 216, 218 between the ends 212, 214 of the inductiveelements 208, 210 may provide the desired capacitance such that theresonant circuit 200 resonates at the desired frequency. For example,the physical dimensions and/or shape of the inductive elements 208, 210may be chosen to provide a desired inductance and the size of the airgaps 216, 218 (i.e., the separation distance between ends 212, 214) maybe chosen to provide a desired capacitance (for example, 2.2 picofarads)such that the resonant circuit 200 resonates at the desired resonantfrequency without capacitive elements 220, 222.

Still referring to FIG. 2, the inductive elements 204, 206 generallyrepresent the input and output terminals of the resonant circuit 200.For convenience, but without limitation, the first inductive element 204may alternatively be referred to herein as the input inductive elementand the second inductive element 206 may alternatively be referred toherein as the output inductive element. As described in greater detailbelow with reference to FIG. 1, in exemplary embodiments, the inputinductive element 204 is coupled to the output node 118 of theoscillator arrangement 102 and the output inductive element 206 iscoupled to the input node 112 of the oscillator arrangement 102.

In the illustrated embodiment of FIG. 2, the input inductive element 204is realized as a rectangular microstrip (or another conductive material)formed on the electrical substrate 201 proximate the first arcuateinductive element 208. The input inductive element 204 is spaced apartor otherwise separated from the inductive element 208 by an air gap 224that functions as a gap capacitor electrically in series between theinductive elements 204, 208. In this regard, the input inductive element204 is capacitively coupled to the inductive element 208 via the gapcapacitance provided by the air gap 224. In an exemplary embodiment, theseparation distance between the inductive elements 204, 208 (e.g., thewidth of the air gap 224) is chosen to be as small as possible toincrease the quality factor (or Q value) of the gap capacitance. Inaccordance with one embodiment, the separation distance between theinductive elements 204, 208 is about 0.01 inches or less.

In a similar manner, the output inductive element 206 is realized asanother rectangular microstrip (or another conductive material) formedon the electrical substrate 201 proximate the second arcuate inductiveelement 210. In the illustrated embodiment, the output inductive element206 is spaced apart or otherwise separated from the inductive element210 by an air gap 226 that functions as a gap capacitor between theinductive elements 206, 210 in a similar manner as described above withrespect to air gap 224. The inductive elements 204, 206 aresubstantially rectangular in shape, and the dimensions of the respectiveinductive elements 204, 206 are chosen to provide a desired input and/oroutput impedance for the resonant circuit 200 at the resonant frequencyof the resonant circuit 200, as described in greater detail below. Itshould be noted that although FIG. 2 depicts air gaps 224, 226 betweenthe both of the inductive elements 204, 206, in accordance with one ormore alternative embodiments, one of the inductive elements 204, 206 maybe electrically connected to the annular resonance structure 202 withouta series capacitance. For example, in accordance with one embodiment,the output inductive element 206 may be formed to physically contact theannular resonance structure 202 and/or arcuate inductive element 210. Inthis regard, the inductive element 206 may be integrally formed with thearcuate inductive element 210 of the annular resonance structure 202. Inan exemplary embodiments, at least one of the inductive elements 204,206 is separated from the annular resonance structure 202 by an air gap224, 226 to increase the quality factor (or Q value) of the resonantcircuit 200. In an exemplary embodiment, the quality factor (or Q value)of the resonant circuit 200 is about 190 or more.

Fabrication of the resonant circuit 200 may be achieved by forming theinductive elements 204, 206, 208, 210 on the electrical substrate 201and forming capacitive elements 220, 222 coupled between thelongitudinal ends 212, 214 of the arcuate inductive elements 208, 210.In this regard, the fabrication process may begin by forming a layer ofconductive material overlying the electrical substrate 201 andselectively removing portions of the conductive material to provide thearcuate inductive elements 208, 210 that define the annular resonancestructure 202 having the voided interior region 203 (e.g., an exposedregion of the electrical substrate 201 substantially encompassed by thearcuate inductive elements 208, 210) and the inductive elements 204, 206proximate the arcuate inductive elements 208, 210. As described above,portions of the conductive material between at least one of theinductive elements 204, 206 and a respective arcuate inductive element208, 210 are removed to provided a gap capacitance in series betweenthat respective inductive element 204, 206 and the respective arcuateinductive element 208, 210 proximate the respective inductive element204, 206. Additionally, portions of the conductive material are removedto provide air gaps 216, 218 between the longitudinal ends 212, 214 ofthe arcuate inductive elements 208, 210. After forming the inductiveelements 204, 206, 208, 210, the fabrication of the resonant circuit 200may be completed by mounting, soldering, or otherwise affixingcapacitive elements 220, 222 to the longitudinal ends 212, 214 of thearcuate inductive elements 208, 210 that span the air gaps 216, 218 andcapacitively couple the arcuate inductive elements 208, 210.

Referring now to FIGS. 1-2, in an exemplary embodiment, the resonantcircuitry 122 in the oscillator system 100 is realized as resonantcircuit 200 such that the annular resonance structure 202 is coupledbetween the output of the amplifier arrangement 120 and the input of theamplifier arrangement 120. In this regard, the input inductive element204 is electrically coupled to node 118 and the output inductive element206 is electrically coupled to node 112. For example, the amplifieroutput impedance matching circuitry 126 may include a microstrip formedon the electrical substrate 201 that is connected to or otherwiseintegral with the input inductive element 204 and the amplifier inputimpedance matching circuitry 124 may include a second microstrip that isconnected to or otherwise integral with the output inductive element206. The physical dimensions of the input inductive element 204 arechosen to match the input impedance of the resonant circuit 200 to theimpedance at node 118, and similarly, the physical dimensions of theoutput inductive element 206 are chosen to match the output impedance ofthe resonant circuit 200 to the impedance at node 112. In this regard,in an exemplary embodiment, the impedances of the impedance matchingcircuitry 124, 126 and the impedances of the inductive elements 204, 206and air gaps 224, 226 are cooperatively configured to provide a desiredgain for the oscillator arrangement 102 at the resonant frequency of theresonant circuitry 122, 200.

FIG. 3 depicts another exemplary embodiment of an oscillator system 300suitable for use with the resonant circuit 200 of FIG. 2. The oscillatorsystem 300 includes, without limitation, an oscillator arrangement 302,frequency tuning circuitry 304, bias circuitry 306, power detectioncircuitry 308, and an output interface 310. Various elements in theoscillator system 300 of FIG. 3 are similar to counterpart elementsdescribed above in the context of the oscillator system 100 of FIG. 1,and accordingly, the details of these common elements will not beredundantly described in the context of FIG. 3. As described above, theelements of the oscillator system 300 are configured to produce anoscillating electromagnetic signal at the output interface 310 having afrequency in the microwave frequency range. It should be understood thatFIG. 3 is a simplified representation of an oscillator system 300 forpurposes of explanation and ease of description, and that practicalembodiments may include other devices and components to provideadditional functions and features, and/or the oscillator system 300 maybe part of a much larger electrical system, as will be understood. Forexample, in practice, the oscillator system 300 will include one or moreinstances of impedance matching circuitry as described above in thecontext of FIG. 1 to match impedances within the oscillator system 300,as will be appreciated in the art.

In the illustrated embodiment of FIG. 3, the amplifier arrangement 320includes a plurality of amplifiers 330, 332, 334 and the oscillatorarrangement 302 includes a power splitter (or power divider) 350configured to divide the input power of the oscillating signal from theresonant circuitry 322 among the amplifiers 330, 332, 334, such that theinput of each amplifier 330, 332, 334 receives a portion of theoscillating signal to be amplified by the amplifier arrangement 320. Inan exemplary embodiment, each amplifier 330, 332, 334 is realized as atransistor having an input (or control) terminal (e.g., a gate terminal)coupled to a respective output of the power splitter 350 and an outputterminal (e.g., a drain terminal) coupled to the oscillator output node318. In an exemplary embodiment, the oscillator arrangement 302 includesa power combiner 360 coupled to the outputs of the amplifiers 330, 332,334 to combine the amplified output signals to produce an amplifiedversion of the oscillating signal generated by the primary amplifier330.

As illustrated in FIG. 3, the bias circuitry 306 is coupled to theamplifiers 330, 332, 334 and controls the DC (or nominal) bias voltagesat the gate and drain terminals of the transistors 330, 332, 334, in asimilar manner as described above in the context of the bias circuitry106 of FIG. 1. In an exemplary embodiment, the bias circuitry 306 isconfigured to bias the primary amplifier 330 to operate in the Class ABmode (e.g., a conduction angle between 180 and 360 degrees) and bias thesecondary amplifiers 332, 334 to operate in the Class C mode (e.g., aconduction angle less than 180 degrees). In accordance with one or moreembodiments, the secondary amplifiers 332, 334 are biased for Class Coperation, such that the secondary amplifiers 332, 334 are turned onwhen the signal power (or voltage) at the input 312 of the primaryamplifier 330 is greater than a threshold amount that indicates that theprimary amplifier 330 is at or near saturation. In this manner, theamplifier arrangement 320 operates similarly to a Doherty amplifier,wherein the secondary amplifiers 332, 334 supplement the output powerprovided by the primary amplifier 330 to increase the power output ofthe oscillator system 300. In other embodiments, the secondaryamplifiers 332, 334 may be biased or otherwise configured to operate indifferent modes other than Class C (e.g., Class AB, Class B, etc.) toachieve different levels of efficiency. Furthermore, it should be notedthe number of secondary amplifiers in a practical embodiment of theoscillator system 300 may vary depending on the needs of a particularapplication (e.g., more or less than two secondary amplifiers may beutilized). In this regard, embodiments of the oscillator system 300 thatinclude only an individual secondary amplifier may be realized withoutthe power splitter 350, with the input of the secondary amplifier beingcoupled to the input of the primary amplifier 330 at node 312.

As illustrated in FIG. 3, the resonant circuitry 322 is coupled betweenthe output node 316 of the primary amplifier 330 and the input node 312of the primary amplifier 330 via the power splitter 350. In an exemplaryembodiment, the resonant circuitry 322 is realized as resonant circuit200 of FIG. 2 and includes an annular resonance structure 202 thatcauses the amplified electrical signals produced by the primaryamplifier 330 to oscillate at or near the resonant frequency of theresonant circuitry 322. The frequency tuning circuitry 304 is coupled tothe input node 312 of the primary amplifier 330 to facilitate adjustmentof the oscillation frequency of the oscillation signals generated by theprimary amplifier 330.

In an exemplary embodiment, the power detection circuitry 308 is coupledbetween the oscillator output 318 and the output interface 310. Thepower detection circuitry 308 generally represents the circuit elements,components, and/or other hardware configured to monitor, measure, orotherwise detect the power of the oscillating signals provided to theoutput interface 310. In an exemplary embodiment, the power detectioncircuitry 308 is also configured to monitor or otherwise measure thepower of signal reflections from the output interface 310. The powerdetection circuitry 308 is coupled to the bias circuitry 306, and inresponse to detecting the power of the signal reflections exceeds athreshold value, the power detection circuitry 308 signals the biascircuitry 306 to turn off or otherwise disable the amplifiers 330, 332,334 of the amplifier arrangement 320. In this manner, the powerdetection circuitry 308 and the bias circuitry 306 are cooperativelyconfigured to protect the amplifiers 330, 332, 334 from signalreflections in response to changes in the impedance at the outputinterface 310.

FIG. 4 depicts another exemplary embodiment of a resonant circuit 400suitable for use as the resonant circuitry 122 in the oscillator system100 of FIG. 1 or the resonant circuitry 322 in the oscillator system 300of FIG. 3. The resonant circuit 400 includes an annular resonancestructure 402 and a pair of inductive elements 404, 406. The annularresonance structure 402 includes a pair of arcuate (or curved) inductiveelements 408, 410 that are capacitively coupled at their longitudinalends 412, 414 by capacitive elements 420, 422 mounted across air gaps416, 418 between the longitudinal ends 412, 414 in a similar manner asdescribed above in the context of FIG. 2. In the illustrated embodimentof FIG. 4, the arcuate inductive elements 408, 410 are substantiallyC-shaped and face each other such that the annular resonance structure402 is substantially circular. The inductive elements 404, 406 areconformal to the annular resonance structure 402, that is, the edges405, 407 of the inductive elements 404, 406 proximate the arcuateinductive elements 408, 410 are arcuate or curved to conform to theouter edges of the arcuate inductive elements 408, 410 to improve thecapacitive coupling between the inductive elements 404, 406 and theannular resonance structure 402. In a similar manner as described abovein the context of FIG. 2, the physical dimensions of the inductiveelements 404, 406, 408, 410 are chosen to provide a desired inductanceand the capacitive elements 420, 422 and air gaps 424, 426 areconfigured to provide a desired capacitance such that the annularresonance structure 402 resonates at a desired frequency with arelatively high quality factor (or Q value).

One advantage of the resonant circuits and oscillator systems describedabove is that the oscillator systems are capable of producing microwavesignals having an equivalent output power to those produced byconventional magnetrons at a lower voltage. For example, an output powergreater than 100 Watts may be achieved with a supply voltage of 28Volts. Additionally, the annular resonant circuitry has a relativelyhigh quality factor (e.g., a Q value greater than 100) that reducesvariations in the oscillating frequency of the output signals withrespect to variations in the supply voltage and/or the load impedance.

For the sake of brevity, conventional techniques related to resonators,amplifiers, biasing, load modulation, impedance matching, powersplitters and/or power combiners, microwave applications, and otherfunctional aspects of the systems (and the individual operatingcomponents of the systems) may not be described in detail herein.Furthermore, the connecting lines shown in the various figures containedherein are intended to represent exemplary functional relationshipsand/or physical couplings between the various elements. It should benoted that many alternative or additional functional relationships orphysical connections may be present in an embodiment of the subjectmatter. In addition, certain terminology may also be used herein for thepurpose of reference only, and thus are not intended to be limiting, andthe terms “first”, “second” and other such numerical terms referring tostructures do not imply a sequence or order unless clearly indicated bythe context.

As used herein, a “node” means any internal or external reference point,connection point, junction, signal line, conductive element, or thelike, at which a given signal, logic level, voltage, data pattern,current, or quantity is present. Furthermore, two or more nodes may berealized by one physical element (and two or more signals can bemultiplexed, modulated, or otherwise distinguished even though receivedor output at a common node).

The foregoing description refers to elements or nodes or features being“connected” or “coupled” together. As used herein, unless expresslystated otherwise, “connected” means that one element is directly joinedto (or directly communicates with) another element, and not necessarilymechanically. Likewise, unless expressly stated otherwise, “coupled”means that one element is directly or indirectly joined to (or directlyor indirectly communicates with) another element, and not necessarilymechanically. Thus, although the schematic shown in the figures depictone exemplary arrangement of elements, additional intervening elements,devices, features, or components may be present in an embodiment of thedepicted subject matter.

In conclusion, systems, devices, and methods configured in accordancewith example embodiments of the invention relate to:

An exemplary embodiment of an oscillator system is provided. Theoscillator system includes a first amplifier having a first amplifierinput and a first amplifier output, and an annular resonance structurecoupled between the first amplifier output and the first amplifierinput. In one embodiment, the oscillator system includes an inductiveelement coupled between the first amplifier and the annular resonancestructure, wherein the inductive element is disposed proximate theannular resonance structure and separated from the annular resonancestructure by an air gap, the inductive element being coupled to theannular resonance structure via a capacitance provided by the air gap.In accordance with one or more exemplary embodiments, the annularresonance structure comprises a first arcuate inductive element and asecond arcuate inductive element capacitively coupled to the firstarcuate inductive element. In one embodiment, the oscillator systemincludes a third inductive element coupled between the first amplifierand the first arcuate inductive element, wherein the third inductiveelement is disposed proximate the first arcuate inductive element andseparated from the first arcuate inductive element by an air gap toprovide a capacitance between the third inductive element and the firstarcuate inductive element, and the third inductive element iscapacitively coupled to the first arcuate inductive element via thecapacitance. In exemplary embodiments, the first arcuate inductiveelement and the second arcuate inductive element are complementary inshape and the annular resonance structure is symmetrical. The firstarcuate inductive element has a first pair of ends and the secondarcuate inductive element has a second pair of ends, wherein the firstpair of ends are capacitively coupled to the second pair of ends. In oneembodiment, the arcuate inductive elements each comprise a substantiallyU-shaped conductive material. In another embodiment, the arcuateinductive elements each comprise a substantially C-shaped conductivematerial. In accordance with one or more embodiments, the oscillatorsystem includes a second amplifier having a second amplifier inputcoupled to the first amplifier input and second amplifier output, and apower combiner having a first input coupled to the first amplifieroutput and a second input coupled to the second amplifier output. In afurther embodiment, the first amplifier is configured to operate inClass AB mode and the second amplifier is configured to operate in ClassC mode. In another embodiment, the oscillator system further includes athird amplifier having a third amplifier input and a third amplifieroutput coupled to a third input of the power combiner, and a powersplitter having an input coupled to the first amplifier input, a firstoutput coupled to the second amplifier input, and a second outputcoupled to the third amplifier input. In one embodiment, a microwaveoven is provided that includes the oscillator system.

Another exemplary embodiment of an oscillator system includes anamplifier having an amplifier input and an amplifier output, andresonant circuitry coupled between the amplifier input and the amplifieroutput, wherein the resonant circuitry includes a first curved inductiveelement and a second curved inductive element capacitively coupled tothe first curved inductive element, and the first curved inductiveelement and the second curved inductive element are cooperativelyconfigured to provide an annular resonance structure. In one embodiment,the oscillator system includes a third inductive element disposedproximate the first curved inductive element and separated from thefirst curved inductive element by an air gap to provide a capacitancebetween the third inductive element and the first curved inductiveelement, wherein the third inductive element is capacitively coupled tothe first curved inductive element via the capacitance. In a furtherembodiment, the oscillator system includes a fourth inductive elementdisposed proximate the second curved inductive element and separatedfrom the second curved inductive element by a second air gap to providea second capacitance between the fourth inductive element and the secondcurved inductive element, wherein the fourth inductive element iscapacitively coupled to the second curved inductive element via thesecond capacitance. In accordance with another embodiment, the firstcurved inductive element and the second curved inductive element arecomplementary in shape and substantially oppose one another. In oneembodiment, the oscillator system includes a first capacitive elementhaving a first terminal coupled to a first longitudinal end of the firstcurved inductive element and a second terminal coupled to a firstlongitudinal end of the second curved inductive element, the firstlongitudinal end of the second curved inductive element facing the firstlongitudinal end of the first curved inductive element, and a secondcapacitive element having a third terminal coupled to a secondlongitudinal end of the first curved inductive element and a fourthterminal coupled to a second longitudinal end of the second curvedinductive element, the second longitudinal end of the second curvedinductive element facing the second longitudinal end of the first curvedinductive element.

In yet another embodiment, a method is provided for forming a resonantcircuit. An exemplary method involves forming a first arcuate inductiveelement on an electrical substrate and forming a second arcuateinductive element on the electrical substrate spaced apart from thefirst arcuate inductive element, the second arcuate inductive elementsubstantially opposing the first arcuate inductive element to provide anannular resonance structure. In one embodiment, the method continues byforming a third inductive element on the electrical substrate proximatethe first arcuate inductive element, wherein the third inductive elementis spaced apart from the first arcuate inductive element by an air gap,the third inductive element being capacitively coupled to the firstarcuate inductive element via the air gap.

While at least one exemplary embodiment has been presented in theforegoing detailed description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or embodiments described herein are not intended tolimit the scope, applicability, or configuration of the claimed subjectmatter in any way. Rather, the foregoing detailed description willprovide those skilled in the art with a convenient road map forimplementing the described embodiment or embodiments. It should beunderstood that various changes can be made in the function andarrangement of elements without departing from the scope defined by theclaims, which includes known equivalents and foreseeable equivalents atthe time of filing this patent application.

What is claimed is:
 1. A method for forming an oscillator arrangementthat includes a resonant circuit, the method comprising: forming a firstinductive element on an electrical substrate; and forming a secondinductive element on the electrical substrate spaced apart from thefirst inductive element, the second inductive element substantiallyopposing the first inductive element to provide an annular resonancestructure, wherein the first and second inductive elements havesubstantially identical electrical characteristics, the first and secondinductive elements curve towards one another so that the annularresonance structure encompasses a voided interior region, a firstlongitudinal end of the first inductive element faces a firstlongitudinal end of the second inductive element across a first air gap,and a second longitudinal end of the first inductive element faces asecond longitudinal end of the second inductive element across a secondair gap.
 2. The method of claim 1, further comprising: forming a thirdinductive element coupled between the first amplifier and the annularresonance structure, wherein the third inductive element is disposedproximate the annular resonance structure and separated from the annularresonance structure by a third air gap, the third inductive elementbeing coupled to the annular resonance structure via a capacitanceprovided by the third air gap.
 3. The method of claim 1, wherein: thefirst inductive element is a first arcuate inductive element, the secondinductive element is a second arcuate inductive element, and wherein themethod further comprises coupling a first capacitive element between thefirst longitudinal ends of the first and second arcuate inductiveelements; and coupling a second capacitive element between the secondlongitudinal ends of the first and second arcuate inductive elements. 4.The method of claim 3, further comprising: forming a third inductiveelement coupled between the first amplifier and the first arcuateinductive element, wherein: the third inductive element is disposedproximate the first arcuate inductive element and separated from thefirst arcuate inductive element by a third air gap to provide acapacitance between the third inductive element and the first arcuateinductive element, and the third inductive element is capacitivelycoupled to the first arcuate inductive element via the capacitance. 5.The method of claim 3, wherein the first arcuate inductive element andthe second arcuate inductive element are complementary in shape.
 6. Themethod of claim 3, wherein the annular resonance structure issymmetrical.
 7. The method of claim 3, wherein: the first arcuateinductive element comprises a first substantially C-shaped conductivematerial; and the second arcuate inductive element comprises a secondsubstantially C-shaped conductive material.
 8. The method of claim 3,wherein: the first arcuate inductive element comprises a firstsubstantially U-shaped conductive material; and the second arcuateinductive element comprises a second substantially U-shaped conductivematerial.
 9. The method of claim 1, wherein the annular resonancestructure is symmetrical.
 10. The method of claim 1, further comprising:coupling an amplifier to the annular resonance structure by coupling thefirst inductive element to an output of the amplifier, and coupling thesecond inductive element to an input of the amplifier.
 11. The method ofclaim 1, further comprising: coupling a first capacitive element betweenthe first longitudinal ends of the first and second inductive elements;and coupling a second capacitive element between the second longitudinalends of the first and second inductive elements.
 12. The method of claim11, further comprising: disposing a third inductive element proximatethe first inductive element and separated from the first inductiveelement by a third air gap to provide a capacitance between the thirdinductive element and the first inductive element, wherein the thirdinductive element is capacitively coupled to the first inductive elementvia the capacitance.
 13. The method of claim 12, further comprising:disposing a fourth inductive element proximate the second inductiveelement and separated from the second inductive element by a fourth airgap to provide a second capacitance between the fourth inductive elementand the second inductive element, wherein the fourth inductive elementis capacitively coupled to the second inductive element via the secondcapacitance.
 14. The method of claim 13, wherein the first inductiveelement and the second inductive element are complementary in shape andsubstantially oppose one another.
 15. The method of claim 11, wherein:the first capacitive element has a first terminal coupled to the firstlongitudinal end of the first inductive element and a second terminalcoupled to the first longitudinal end of the second inductive element;and the second capacitive element has a third terminal coupled to thesecond longitudinal end of the first inductive element and a fourthterminal coupled to the second longitudinal end of the second inductiveelement.